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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<title>Xapian: API Documentation: Xapian::BM25Weight Class Reference</title>
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<li class="navelem"><a class="el" href="namespaceXapian.html">Xapian</a></li><li class="navelem"><a class="el" href="classXapian_1_1BM25Weight.html">BM25Weight</a></li> </ul>
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<div class="title">Xapian::BM25Weight Class Reference</div> </div>
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<p><a class="el" href="classXapian_1_1Weight.html" title="Abstract base class for weighting schemes. ">Xapian::Weight</a> subclass implementing the BM25 probabilistic formula.
<a href="classXapian_1_1BM25Weight.html#details">More...</a></p>
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<img id="dynsection-0-trigger" src="closed.png" alt="+"/> Inheritance diagram for Xapian::BM25Weight:</div>
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<div class="center"><img src="classXapian_1_1BM25Weight__inherit__graph.png" border="0" usemap="#Xapian_1_1BM25Weight_inherit__map" alt="Inheritance graph"/></div>
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<area shape="rect" id="node2" href="classXapian_1_1Weight.html" title="Abstract base class for weighting schemes. " alt="" coords="23,5,132,35"/></map>
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<table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="pub-methods"></a>
Public Member Functions</h2></td></tr>
<tr class="memitem:a40ccbf44b5aabe58c1258eb4abcd4df1"><td class="memItemLeft" align="right" valign="top"> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1BM25Weight.html#a40ccbf44b5aabe58c1258eb4abcd4df1">BM25Weight</a> (double k1, double k2, double k3, double b, double min_normlen)</td></tr>
<tr class="memdesc:a40ccbf44b5aabe58c1258eb4abcd4df1"><td class="mdescLeft"> </td><td class="mdescRight">Construct a <a class="el" href="classXapian_1_1BM25Weight.html" title="Xapian::Weight subclass implementing the BM25 probabilistic formula. ">BM25Weight</a>. <a href="#a40ccbf44b5aabe58c1258eb4abcd4df1">More...</a><br/></td></tr>
<tr class="separator:a40ccbf44b5aabe58c1258eb4abcd4df1"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a943fdc83495a97f7d6af1208f5b26052"><td class="memItemLeft" align="right" valign="top">std::string </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1BM25Weight.html#a943fdc83495a97f7d6af1208f5b26052">name</a> () const </td></tr>
<tr class="memdesc:a943fdc83495a97f7d6af1208f5b26052"><td class="mdescLeft"> </td><td class="mdescRight">Return the name of this weighting scheme. <a href="#a943fdc83495a97f7d6af1208f5b26052">More...</a><br/></td></tr>
<tr class="separator:a943fdc83495a97f7d6af1208f5b26052"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a2dd2eb60deb5690e471d68f4c7fc3203"><td class="memItemLeft" align="right" valign="top">std::string </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1BM25Weight.html#a2dd2eb60deb5690e471d68f4c7fc3203">serialise</a> () const </td></tr>
<tr class="memdesc:a2dd2eb60deb5690e471d68f4c7fc3203"><td class="mdescLeft"> </td><td class="mdescRight">Return this object's parameters serialised as a single string. <a href="#a2dd2eb60deb5690e471d68f4c7fc3203">More...</a><br/></td></tr>
<tr class="separator:a2dd2eb60deb5690e471d68f4c7fc3203"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a8a9f0c48f4229aa0d62feff5f496dc78"><td class="memItemLeft" align="right" valign="top"><a class="el" href="classXapian_1_1BM25Weight.html">BM25Weight</a> * </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1BM25Weight.html#a8a9f0c48f4229aa0d62feff5f496dc78">unserialise</a> (const std::string &s) const </td></tr>
<tr class="memdesc:a8a9f0c48f4229aa0d62feff5f496dc78"><td class="mdescLeft"> </td><td class="mdescRight">Unserialise parameters. <a href="#a8a9f0c48f4229aa0d62feff5f496dc78">More...</a><br/></td></tr>
<tr class="separator:a8a9f0c48f4229aa0d62feff5f496dc78"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a4fe48617e7db67232208a00b94878f54"><td class="memItemLeft" align="right" valign="top"><a class="el" href="namespaceXapian.html#acac12803afc9e24ee5141c119acb8884">Xapian::weight</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1BM25Weight.html#a4fe48617e7db67232208a00b94878f54">get_sumpart</a> (<a class="el" href="namespaceXapian.html#a72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> wdf, <a class="el" href="namespaceXapian.html#a72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> doclen) const </td></tr>
<tr class="memdesc:a4fe48617e7db67232208a00b94878f54"><td class="mdescLeft"> </td><td class="mdescRight">Calculate the weight contribution for this object's term to a document. <a href="#a4fe48617e7db67232208a00b94878f54">More...</a><br/></td></tr>
<tr class="separator:a4fe48617e7db67232208a00b94878f54"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:af23907adc06e73cdf1228fc616a2fda2"><td class="memItemLeft" align="right" valign="top"><a class="el" href="namespaceXapian.html#acac12803afc9e24ee5141c119acb8884">Xapian::weight</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1BM25Weight.html#af23907adc06e73cdf1228fc616a2fda2">get_maxpart</a> () const </td></tr>
<tr class="memdesc:af23907adc06e73cdf1228fc616a2fda2"><td class="mdescLeft"> </td><td class="mdescRight">Return an upper bound on what <a class="el" href="classXapian_1_1BM25Weight.html#a4fe48617e7db67232208a00b94878f54" title="Calculate the weight contribution for this object's term to a document. ">get_sumpart()</a> can return for any document. <a href="#af23907adc06e73cdf1228fc616a2fda2">More...</a><br/></td></tr>
<tr class="separator:af23907adc06e73cdf1228fc616a2fda2"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a6992ef2cd23a095d607b70aa2076850b"><td class="memItemLeft" align="right" valign="top"><a class="el" href="namespaceXapian.html#acac12803afc9e24ee5141c119acb8884">Xapian::weight</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1BM25Weight.html#a6992ef2cd23a095d607b70aa2076850b">get_sumextra</a> (<a class="el" href="namespaceXapian.html#a72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> doclen) const </td></tr>
<tr class="memdesc:a6992ef2cd23a095d607b70aa2076850b"><td class="mdescLeft"> </td><td class="mdescRight">Calculate the term-independent weight component for a document. <a href="#a6992ef2cd23a095d607b70aa2076850b">More...</a><br/></td></tr>
<tr class="separator:a6992ef2cd23a095d607b70aa2076850b"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a7c91481891313e089eb38bf1a9a83029"><td class="memItemLeft" align="right" valign="top"><a class="el" href="namespaceXapian.html#acac12803afc9e24ee5141c119acb8884">Xapian::weight</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1BM25Weight.html#a7c91481891313e089eb38bf1a9a83029">get_maxextra</a> () const </td></tr>
<tr class="memdesc:a7c91481891313e089eb38bf1a9a83029"><td class="mdescLeft"> </td><td class="mdescRight">Return an upper bound on what <a class="el" href="classXapian_1_1BM25Weight.html#a6992ef2cd23a095d607b70aa2076850b" title="Calculate the term-independent weight component for a document. ">get_sumextra()</a> can return for any document. <a href="#a7c91481891313e089eb38bf1a9a83029">More...</a><br/></td></tr>
<tr class="separator:a7c91481891313e089eb38bf1a9a83029"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="inherit_header pub_methods_classXapian_1_1Weight"><td colspan="2" onclick="javascript:toggleInherit('pub_methods_classXapian_1_1Weight')"><img src="closed.png" alt="-"/> Public Member Functions inherited from <a class="el" href="classXapian_1_1Weight.html">Xapian::Weight</a></td></tr>
<tr class="memitem:adcc0dd3e0c762597e89720043440a0bd inherit pub_methods_classXapian_1_1Weight"><td class="memItemLeft" align="right" valign="top">virtual </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#adcc0dd3e0c762597e89720043440a0bd">~Weight</a> ()</td></tr>
<tr class="memdesc:adcc0dd3e0c762597e89720043440a0bd inherit pub_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">Virtual destructor, because we have virtual methods. <a href="#adcc0dd3e0c762597e89720043440a0bd">More...</a><br/></td></tr>
<tr class="separator:adcc0dd3e0c762597e89720043440a0bd inherit pub_methods_classXapian_1_1Weight"><td class="memSeparator" colspan="2"> </td></tr>
</table><table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="inherited"></a>
Additional Inherited Members</h2></td></tr>
<tr class="inherit_header pro_types_classXapian_1_1Weight"><td colspan="2" onclick="javascript:toggleInherit('pro_types_classXapian_1_1Weight')"><img src="closed.png" alt="-"/> Protected Types inherited from <a class="el" href="classXapian_1_1Weight.html">Xapian::Weight</a></td></tr>
<tr class="memitem:ae3c11f1d2d96a18e0eb9b9b31c5c5479 inherit pro_types_classXapian_1_1Weight"><td class="memItemLeft" align="right" valign="top">enum  </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#ae3c11f1d2d96a18e0eb9b9b31c5c5479">stat_flags</a> </td></tr>
<tr class="memdesc:ae3c11f1d2d96a18e0eb9b9b31c5c5479"><td class="mdescLeft"> </td><td class="mdescRight">Stats which the weighting scheme can use (see <em><a class="el" href="classXapian_1_1Weight.html#a77b1424d5f5a5b2d4848175979da6475" title="Tell Xapian that your subclass will want a particular statistic. ">need_stat()</a></em>). <br/></td></tr>
<tr class="separator:ae3c11f1d2d96a18e0eb9b9b31c5c5479 inherit pro_types_classXapian_1_1Weight"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="inherit_header pro_methods_classXapian_1_1Weight"><td colspan="2" onclick="javascript:toggleInherit('pro_methods_classXapian_1_1Weight')"><img src="closed.png" alt="-"/> Protected Member Functions inherited from <a class="el" href="classXapian_1_1Weight.html">Xapian::Weight</a></td></tr>
<tr class="memitem:a77b1424d5f5a5b2d4848175979da6475 inherit pro_methods_classXapian_1_1Weight"><td class="memItemLeft" align="right" valign="top">void </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#a77b1424d5f5a5b2d4848175979da6475">need_stat</a> (<a class="el" href="classXapian_1_1Weight.html#ae3c11f1d2d96a18e0eb9b9b31c5c5479">stat_flags</a> flag)</td></tr>
<tr class="memdesc:a77b1424d5f5a5b2d4848175979da6475 inherit pro_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">Tell <a class="el" href="namespaceXapian.html" title="The Xapian namespace contains public interfaces for the Xapian library. ">Xapian</a> that your subclass will want a particular statistic. <a href="#a77b1424d5f5a5b2d4848175979da6475">More...</a><br/></td></tr>
<tr class="separator:a77b1424d5f5a5b2d4848175979da6475 inherit pro_methods_classXapian_1_1Weight"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:aa7acc105949dcb3b8b343a598dd01487 inherit pro_methods_classXapian_1_1Weight"><td class="memItemLeft" align="right" valign="top"> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#aa7acc105949dcb3b8b343a598dd01487">Weight</a> (const <a class="el" href="classXapian_1_1Weight.html">Weight</a> &)</td></tr>
<tr class="memdesc:aa7acc105949dcb3b8b343a598dd01487 inherit pro_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">Don't allow copying. <a href="#aa7acc105949dcb3b8b343a598dd01487">More...</a><br/></td></tr>
<tr class="separator:aa7acc105949dcb3b8b343a598dd01487 inherit pro_methods_classXapian_1_1Weight"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a48e8f4d351f2a090bcec111513833e0f inherit pro_methods_classXapian_1_1Weight"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="a48e8f4d351f2a090bcec111513833e0f"></a>
 </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#a48e8f4d351f2a090bcec111513833e0f">Weight</a> ()</td></tr>
<tr class="memdesc:a48e8f4d351f2a090bcec111513833e0f inherit pro_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">Default constructor, needed by subclass constructors. <br/></td></tr>
<tr class="separator:a48e8f4d351f2a090bcec111513833e0f inherit pro_methods_classXapian_1_1Weight"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:aa2e23f50f21b1bc185f90b1e9cb7a7f3 inherit pro_methods_classXapian_1_1Weight"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="aa2e23f50f21b1bc185f90b1e9cb7a7f3"></a>
<a class="el" href="namespaceXapian.html#a7f30aa95f0c42b117dafaf66ba24241d">Xapian::doccount</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#aa2e23f50f21b1bc185f90b1e9cb7a7f3">get_collection_size</a> () const </td></tr>
<tr class="memdesc:aa2e23f50f21b1bc185f90b1e9cb7a7f3 inherit pro_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">The number of documents in the collection. <br/></td></tr>
<tr class="separator:aa2e23f50f21b1bc185f90b1e9cb7a7f3 inherit pro_methods_classXapian_1_1Weight"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a8a8cce67a8493930d450b7146ef7579d inherit pro_methods_classXapian_1_1Weight"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="a8a8cce67a8493930d450b7146ef7579d"></a>
<a class="el" href="namespaceXapian.html#a7f30aa95f0c42b117dafaf66ba24241d">Xapian::doccount</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#a8a8cce67a8493930d450b7146ef7579d">get_rset_size</a> () const </td></tr>
<tr class="memdesc:a8a8cce67a8493930d450b7146ef7579d inherit pro_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">The number of documents marked as relevant. <br/></td></tr>
<tr class="separator:a8a8cce67a8493930d450b7146ef7579d inherit pro_methods_classXapian_1_1Weight"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a918940bab1dc710ecb97da04f5fa6385 inherit pro_methods_classXapian_1_1Weight"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="a918940bab1dc710ecb97da04f5fa6385"></a>
<a class="el" href="namespaceXapian.html#a63b13d3a36fcab9975658e32643d86b5">Xapian::doclength</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#a918940bab1dc710ecb97da04f5fa6385">get_average_length</a> () const </td></tr>
<tr class="memdesc:a918940bab1dc710ecb97da04f5fa6385 inherit pro_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">The average length of a document in the collection. <br/></td></tr>
<tr class="separator:a918940bab1dc710ecb97da04f5fa6385 inherit pro_methods_classXapian_1_1Weight"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a92938b9a4e06cc4064d175678cbf89db inherit pro_methods_classXapian_1_1Weight"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="a92938b9a4e06cc4064d175678cbf89db"></a>
<a class="el" href="namespaceXapian.html#a7f30aa95f0c42b117dafaf66ba24241d">Xapian::doccount</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#a92938b9a4e06cc4064d175678cbf89db">get_termfreq</a> () const </td></tr>
<tr class="memdesc:a92938b9a4e06cc4064d175678cbf89db inherit pro_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">The number of documents which this term indexes. <br/></td></tr>
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<a class="el" href="namespaceXapian.html#a7f30aa95f0c42b117dafaf66ba24241d">Xapian::doccount</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#a1e6c2200a16fe2ed1631e498b0938de8">get_reltermfreq</a> () const </td></tr>
<tr class="memdesc:a1e6c2200a16fe2ed1631e498b0938de8 inherit pro_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">The number of relevant documents which this term indexes. <br/></td></tr>
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<a class="el" href="namespaceXapian.html#a72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#a346c098a7aa0e4834a2d0289f2095bec">get_query_length</a> () const </td></tr>
<tr class="memdesc:a346c098a7aa0e4834a2d0289f2095bec inherit pro_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">The length of the query. <br/></td></tr>
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<a class="el" href="namespaceXapian.html#a72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#a764637daf40de00c390c2248fb0d9669">get_wqf</a> () const </td></tr>
<tr class="memdesc:a764637daf40de00c390c2248fb0d9669 inherit pro_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">The within-query-frequency of this term. <br/></td></tr>
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<tr class="memitem:a6fdebced528afecf5709eb94aae8a03b inherit pro_methods_classXapian_1_1Weight"><td class="memItemLeft" align="right" valign="top"><a class="el" href="namespaceXapian.html#a72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#a6fdebced528afecf5709eb94aae8a03b">get_doclength_upper_bound</a> () const </td></tr>
<tr class="memdesc:a6fdebced528afecf5709eb94aae8a03b inherit pro_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">An upper bound on the maximum length of any document in the database. <a href="#a6fdebced528afecf5709eb94aae8a03b">More...</a><br/></td></tr>
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<tr class="memitem:ae7174b4c8b66f72f8d7a8086ca4fb476 inherit pro_methods_classXapian_1_1Weight"><td class="memItemLeft" align="right" valign="top"><a class="el" href="namespaceXapian.html#a72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#ae7174b4c8b66f72f8d7a8086ca4fb476">get_doclength_lower_bound</a> () const </td></tr>
<tr class="memdesc:ae7174b4c8b66f72f8d7a8086ca4fb476 inherit pro_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">A lower bound on the minimum length of any document in the database. <a href="#ae7174b4c8b66f72f8d7a8086ca4fb476">More...</a><br/></td></tr>
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<tr class="memitem:aed86f1d362deac4a1492480ca28c788f inherit pro_methods_classXapian_1_1Weight"><td class="memItemLeft" align="right" valign="top"><a class="el" href="namespaceXapian.html#a72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1Weight.html#aed86f1d362deac4a1492480ca28c788f">get_wdf_upper_bound</a> () const </td></tr>
<tr class="memdesc:aed86f1d362deac4a1492480ca28c788f inherit pro_methods_classXapian_1_1Weight"><td class="mdescLeft"> </td><td class="mdescRight">An upper bound on the wdf of this term. <a href="#aed86f1d362deac4a1492480ca28c788f">More...</a><br/></td></tr>
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<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
<div class="textblock"><p><a class="el" href="classXapian_1_1Weight.html" title="Abstract base class for weighting schemes. ">Xapian::Weight</a> subclass implementing the BM25 probabilistic formula. </p>
</div><h2 class="groupheader">Constructor & Destructor Documentation</h2>
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<td class="memname">Xapian::BM25Weight::BM25Weight </td>
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<td class="paramtype">double </td>
<td class="paramname"><em>k1</em>, </td>
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<td class="paramtype">double </td>
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<td class="paramtype">double </td>
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<td class="paramtype">double </td>
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<p>Construct a <a class="el" href="classXapian_1_1BM25Weight.html" title="Xapian::Weight subclass implementing the BM25 probabilistic formula. ">BM25Weight</a>. </p>
<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramname">k1</td><td>A non-negative parameter controlling how influential within-document-frequency (wdf) is. k1=0 means that wdf doesn't affect the weights. The larger k1 is, the more wdf influences the weights. (default 1)</td></tr>
<tr><td class="paramname">k2</td><td>A non-negative parameter which controls the strength of a correction factor which depends upon query length and normalised document length. k2=0 disable this factor; larger k2 makes it stronger. (default 0)</td></tr>
<tr><td class="paramname">k3</td><td>A non-negative parameter controlling how influential within-query-frequency (wqf) is. k3=0 means that wqf doesn't affect the weights. The larger k3 is, the more wqf influences the weights. (default 1)</td></tr>
<tr><td class="paramname">b</td><td>A parameter between 0 and 1, controlling how strong the document length normalisation of wdf is. 0 means no normalisation; 1 means full normalisation. (default 0.5)</td></tr>
<tr><td class="paramname">min_normlen</td><td>A parameter specifying a minimum value for normalised document length. Normalised document length values less than this will be clamped to this value, helping to prevent very short documents getting large weights. (default 0.5) </td></tr>
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<h2 class="groupheader">Member Function Documentation</h2>
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<td class="memname"><a class="el" href="namespaceXapian.html#acac12803afc9e24ee5141c119acb8884">Xapian::weight</a> Xapian::BM25Weight::get_maxextra </td>
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<p>Return an upper bound on what <a class="el" href="classXapian_1_1BM25Weight.html#a6992ef2cd23a095d607b70aa2076850b" title="Calculate the term-independent weight component for a document. ">get_sumextra()</a> can return for any document. </p>
<p>This information is used by the matcher to perform various optimisations, so strive to make the bound as tight as possible. </p>
<p>Implements <a class="el" href="classXapian_1_1Weight.html#aca641ecc2f5645666820f864d243f46d">Xapian::Weight</a>.</p>
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<p>Return an upper bound on what <a class="el" href="classXapian_1_1BM25Weight.html#a4fe48617e7db67232208a00b94878f54" title="Calculate the weight contribution for this object's term to a document. ">get_sumpart()</a> can return for any document. </p>
<p>This information is used by the matcher to perform various optimisations, so strive to make the bound as tight as possible. </p>
<p>Implements <a class="el" href="classXapian_1_1Weight.html#af37e797fa12bb915f73b20b953a132b7">Xapian::Weight</a>.</p>
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<td class="memname"><a class="el" href="namespaceXapian.html#acac12803afc9e24ee5141c119acb8884">Xapian::weight</a> Xapian::BM25Weight::get_sumextra </td>
<td>(</td>
<td class="paramtype"><a class="el" href="namespaceXapian.html#a72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> </td>
<td class="paramname"><em>doclen</em></td><td>)</td>
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<p>Calculate the term-independent weight component for a document. </p>
<p>The parameter gives information about the document which may be used in the calculations:</p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramname">doclen</td><td>The document's length (unnormalised). </td></tr>
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<p>Implements <a class="el" href="classXapian_1_1Weight.html#a8c29b15b875e5666ac8b94c9a39e962f">Xapian::Weight</a>.</p>
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<td class="memname"><a class="el" href="namespaceXapian.html#acac12803afc9e24ee5141c119acb8884">Xapian::weight</a> Xapian::BM25Weight::get_sumpart </td>
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<td class="paramtype"><a class="el" href="namespaceXapian.html#a72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> </td>
<td class="paramname"><em>wdf</em>, </td>
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<td class="paramtype"><a class="el" href="namespaceXapian.html#a72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> </td>
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<p>Calculate the weight contribution for this object's term to a document. </p>
<p>The parameters give information about the document which may be used in the calculations:</p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramname">wdf</td><td>The within document frequency of the term in the document. </td></tr>
<tr><td class="paramname">doclen</td><td>The document's length (unnormalised). </td></tr>
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<p>Implements <a class="el" href="classXapian_1_1Weight.html#a8c6beb18e2c08cbc2ae61ec9d808ed9e">Xapian::Weight</a>.</p>
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<p>Return the name of this weighting scheme. </p>
<p>This name is used by the remote backend. It is passed along with the serialised parameters to the remote server so that it knows which class to create.</p>
<p>Return the full namespace-qualified name of your class here - if your class is called FooWeight, return "FooWeight" from this method (<a class="el" href="classXapian_1_1BM25Weight.html" title="Xapian::Weight subclass implementing the BM25 probabilistic formula. ">Xapian::BM25Weight</a> returns "Xapian::BM25Weight" here).</p>
<p>If you don't want to support the remote backend, you can use the default implementation which simply returns an empty string. </p>
<p>Reimplemented from <a class="el" href="classXapian_1_1Weight.html#aafd3b445fb1955aae3d7c32aae3ba7b4">Xapian::Weight</a>.</p>
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<p>Return this object's parameters serialised as a single string. </p>
<p>If you don't want to support the remote backend, you can use the default implementation which simply throws <a class="el" href="classXapian_1_1UnimplementedError.html" title="UnimplementedError indicates an attempt to use an unimplemented feature. ">Xapian::UnimplementedError</a>. </p>
<p>Reimplemented from <a class="el" href="classXapian_1_1Weight.html#acf568da52a87e6a6786400dbd0a79edf">Xapian::Weight</a>.</p>
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<td class="memname"><a class="el" href="classXapian_1_1BM25Weight.html">BM25Weight</a>* Xapian::BM25Weight::unserialise </td>
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<p>Unserialise parameters. </p>
<p>This method unserialises parameters serialised by the <em><a class="el" href="classXapian_1_1BM25Weight.html#a2dd2eb60deb5690e471d68f4c7fc3203" title="Return this object's parameters serialised as a single string. ">serialise()</a></em> method and allocates and returns a new object initialised with them.</p>
<p>If you don't want to support the remote backend, you can use the default implementation which simply throws <a class="el" href="classXapian_1_1UnimplementedError.html" title="UnimplementedError indicates an attempt to use an unimplemented feature. ">Xapian::UnimplementedError</a>.</p>
<p>Note that the returned object will be deallocated by <a class="el" href="namespaceXapian.html" title="The Xapian namespace contains public interfaces for the Xapian library. ">Xapian</a> after use with "delete". If you want to handle the deletion in a special way (for example when wrapping the <a class="el" href="namespaceXapian.html" title="The Xapian namespace contains public interfaces for the Xapian library. ">Xapian</a> API for use from another language) then you can define a static <code>operator delete</code> method in your subclass as shown here: <a href="http://trac.xapian.org/ticket/554#comment:1">http://trac.xapian.org/ticket/554#comment:1</a></p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramname">s</td><td>A string containing the serialised parameters. </td></tr>
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<p>Reimplemented from <a class="el" href="classXapian_1_1Weight.html#a031c3e0db3ae50e801b324e71a44c140">Xapian::Weight</a>.</p>
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<hr/>The documentation for this class was generated from the following file:<ul>
<li>xapian/<a class="el" href="weight_8h.html">weight.h</a></li>
</ul>
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<address><small>
Documentation for Xapian (version 1.2.19).<br>
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<a href="http://www.doxygen.org/">Doxygen 1.8.5</a>.
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